NITROGEN ABUNDANCES IN CARBON-RICH STARS THAT ARE PROGENITORS TO PLANETARY-NEBULAE

We examine published data for carbon stars losing more than 10(-6) M. yr-1 in the neighborhood of the Sun. The stars with higher terminal velocities have significantly higher fluxes of the J = 1-0 emission line of HCN relative to their infrared continuum emission at 60-mu-m. We argue that this result is probably a reflection of a higher nitrogen abundance by perhaps a factor of 10 in these outflows. Such a high nitrogen abundance is consistent with the hypothesis that the high terminal velocity carbon stars have more massive main-sequence progenitors than average; these high terminal velocity carbon stars may, themselves, be the progenitors of type I planetary nebulae which display enhanced nitrogen abundances.